Many detergents comprising an anionic surfactant, such as an alkylbenzenesulfonate, as a main component have been prepared from the viewpoints of economic advantage, foaming property and the like. As a process for preparing the detergent particles as mentioned above, there has been employed a process in which an acid precursor of the above anionic surfactant is in situ dry-neutralized with a water-soluble solid alkali inorganic substance, such as sodium carbonate, instead of directly adding the surfactant.
For instance, a process of producing a detergent composition comprising the steps of dry-neutralizing components in a high speed mixer and/or granulator at a temperature of 55° C. or less, and thereafter adding a liquid binder thereto to carry out granulation (see Japanese Patent Laid-Open No. Hei 3-33199); a process of producing a detergent composition comprising the steps of dry-neutralizing components in a high speed mixer and/or granulator at a temperature of 55° C. or more, and then adding a liquid binder thereto to carry out granulation (see Japanese Patent Laid-Open No. Hei 4-363398); and a process of producing a detergent composition comprising dry-neutralizing components in a continuous-type high-speed mixer and then increasing the bulk density with a moderate-speed mixer, and subsequently cooling and/or drying the product to form into granules (see Japanese Patent Laid-Open No. Hei 3-146599) have been disclosed.
However, when the detergent particle is produced by these processes, in order to suppress the particle from being aggregated and/or becoming coarse due to the adhesive property of the anionic surfactant produced by the neutralization, it is necessary to keep its granular shape by operating the agitation mechanism for mixing and the cutting mechanism for disintegration and/or dispersion at high speeds. In this case, the detergent particle having a desired small particle size can be prepared by optimizing the agitation and/or cutting conditions. However, it would be difficult to efficiently obtain the detergent particle, and the particle size distribution of the resulting particle would become wider.
As a process for eliminating these problems, a method for preparing a detergent particle having a small particle size at a high yield in which the adhesive property of the anionic surfactant can be suppressed by containing an inorganic acid in the acid precursor and the content of the anionic surfactant can be increased (see WO 98/10052). However, there have yet remain the problems of disintegrating the aggregate by agitation and/or cutting and making the particle size smaller, so that there are much room for improvement in the efficiency and the obtainment of a sharper particle size distribution.
As mentioned above, the process according to dry-neutralization is suitable for conveniently preparing detergent particles comprising an anionic surfactant as a main component. In the conventional process, the process is basically carried out by granulating raw materials with disintegrating, thereby making it difficult to efficiently obtain detergent particles having a sharp particle size distribution in a relatively small particle size range.
In addition, with regard to the dissolubility, according to the conventional process as described above, the detergent particles comprise non-hollow particles having a structure in which solid particles are connected by a large continuous layer of the anionic surfactant. Therefore, it would not be easy to improve the dissolubility.
Having a sharp particle size distribution in the detergent has an advantage of not only giving excellent external appearance but also improving its flowability. Also, a detergent comprising an anionic surfactant as a main component may be used for handwashing in many cases, so that the users' convenience is improved by increasing the dissolubility. Therefore, a sharper particle size distribution and more improved dissolubility have been desired in detergent particles comprising an anionic surfactant as a main component obtained by dry-neutralization.
An object of the present invention is to provide detergent particles having excellent storage stability, dissolubility and sharp particle size distribution, a process for preparing the detergent particles, base particles and a detergent composition comprising the detergent particles.
These and other objects of the present invention will be apparent from the following description.